Evolution of the turnover frequency, ν_m, and the turnover flux density, S_m, for a model with b = 1.5, s = 2.5, ρ = 1, k = 3.0, and d = 0. The top panel shows the evolution of the flare in the (ν_m–S_m) plane (the time evolution is from the bottom right, to the centre and to the bottom left). The black dashed line indicates the path along which ν_m and S_m (red dots) evolve. The slopes of the different stages are given in the plot. The red lines correspond to SSA spectra computed for different times (position along the spectral evolution path). The middle panel shows the temporal evolution of ν_m, and the bottom panel displays the temporal evolution of S_m.